(Customization): Use xref to elisp manual for non-TeX output.

(Customization): Use xref to elisp manual for non-TeX output.
(Minor Modes): Update.
(Customization Groups, Changing a Variable, Face Customization):
Update for new appearance of Custom buffers.
(Changing a Variable): `custom-buffer-done-function' has been
replaced by `custom-buffer-done-kill'.
(Specific Customization): In the `customize-group' buffer, a
subgroup's contents are not "hidden".  They are not included at
all.  They have no [Show] button.
(Mouse Buttons): Add pxref to description of mouse event lists in
Elisp manual.  Add `menu-bar' and `header-line' dummy prefix keys.
(Find Init): Emacs now looks for ~/.emacs.d/init.el instead of
~/.emacs.d/.emacs, if it can not find ~/.emacs(.el).